The invention relates to a dishwasher, in particular a domestic dishwasher, having a detergent-solution pump for pumping dirty washing liquid out of a washing compartment and having a discharge line that is connected to the detergent-solution pump on the pressure side and linked to a venting shaft located above the washing compartment's topmost liquid level, with a first valve that is closed when the detergent-solution pump is operating and otherwise open being located in the venting shaft.
A generic dishwasher of said type is known from DE 40 40 967 A1. It further has a second valve located in the discharge line, with said second valve being kept closed when the detergent-solution pump has not been actuated. The first valve serves to provide ventilating of the detergent-solution pump, as a result of which any air trapped therein can escape via the venting shaft so that the detergent-solution pump can immediately after being switched on start conveying the washing liquid requiring to be pumped away. The second valve serves to prevent washing liquid that is being conveyed by the detergent-solution pump into the discharge line from flowing back into the washing compartment.
Detergent-solution pumps of domestic dishwashers are usually not adequately able to convey air. At the end of a program section during which liquid is conveyed the detergent-solution pump is in the case of domestic dishwashers usually operated for a predefined running time for pumping away dirty washing liquid. When air is trapped in the detergent-solution pump a greater part of its predefined running time is owing to its low air-conveying capability needed for conveying the trapped air before the liquid requiring to be pumped away can be pumped away. It is consequently not possible for the entire volume of liquid requiring to be pumped away to be pumped away.
Depending on the detergent-solution pump's specific structural design the situation may even arise of its not being at all possible to convey liquid owing to air trapped in the detergent-solution pump. That can occur particularly in the case of detergent-solution pumps operated by means of a synchronous motor where the impeller wheel's direction of rotation is for design reasons indeterminable. Detergent-solution pumps of said kind therefore have their outflow stub pipe arranged as a rule centrally on the detergent-solution pump's pump housing. When an air pocket is trapped in the pump housing the situation can therein arise that washing liquid will through the impeller wheel's rotation be pressed against the pump housing's outer side owing to the greater mass compared with air, while air accumulates inside. That ring of air on the pump wheel will prevent a sufficient build-up of pressure for opening the second valve so that no washing liquid can be pumped away.
Further filling with washing liquid during an ensuing program section can in the worst case lead to overfilling and overflowing of the domestic dishwasher. In the event of a fault, the dishes will in any case always be re-soiled by the dirty washing liquid still remaining from the previous program section in proportion to the remaining, soiled volume of washing liquid.